The present invention relates to a speed change lever device for a bicycle, and more particularly to improvements in the speed change lever device which cooperates with a rear derailleur and a multi-speed free wheel assembly having a plurality of sprocket wheels of different diameter mounted on a rear axle of a bicycle, in order to switch over the running drive chain from one sprocket wheel to another for effecting the speed change.
In the art of bicycle speed change lever devices, it is well known that the lever handle must be retained in a selected speed gear position by such a retaining force as at least greater than the known tensile force of the rear derailleur. It is apparent that if the retaining force is considerably greater than said tensile force, it is very difficult to operate the lever handle quite smoothly. On the other hand, if the retaining force is smaller than the tensile force, the lever handle cannot be maintained in a selected speed gear position. Therefore, one of the important problems in the field is how to obtain the proper retaining force. Another important problem in the field is how to bring the handle lever selectively into an accurate speed gear position and retain it therein.
In order to solve the first problem, provision of a ratchet mechanism has proved to be effective, as disclosed in U.S. Pat. No. 3,693,469 to Ozaki. However, according to the method by Ozaki, the second problem remains unsolved. While, in order to solve the second problem, such a mechanism has been proposed which includes a clip-stop ball, a plurality of circular holes formed in a fixed control plate, and a spring element adapted for normally pressing said ball into selected one of said holes, as disclosed in U.S. Pat Nos. 3,362,238 to Hayashi, et al and 3,394,604 to Kimura. However, according to the clip-stop type methods, the first problem remains unsolved. According to the Kimura's method, the handle lever is retained in a desired position merely by forced engagement of the ball with one of the circular holes. Therefore, a considerable physical force is required for forcibly disengaging the ball out of the hole, since the ball must be forcibly rolled out of the hole by such a force applied in the direction transverse to the rolling out direction of the ball, in addition to the fact that said control plate must be forcibly pressed away by the ball so as to provide a certain space corresponding to the diameter of the ball for permitting the rolling out thereof. Further, when adjustment is made for securing a desired larger retaining force, it is always accompanied by undesirable increase of the force required for forcibly taking the ball out of the hole. Thus, it is difficult to achieve the very smooth speed change operation of the lever handle.
Accordingly, it is an object of the present invention to eliminate all of the above-discussed prior art deficiencies.
Another object of the invention is to provide an improved bicycle speed change lever device which can be retained properly in a selected speed gear position.
A further object of the invention is to provide an improved bicycle speed change lever device which can be operated quite smoothly with minimum physical force of an operator.
A still further object of the invention is to provide an improved bicycle speed change lever device which can be selectively brought into an accurate speed gear position and retained therein.
Other objects, features and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.